Tire rasp blade

ABSTRACT

A tire rasp blade is provided with an elongated planar body having a working portion comprising a plurality of uniformly and closely spaced teeth which define an arcuate working perimeter. Each of the teeth has a base and a working edge and is separated from neighboring teeth by generally elliptical primary cutouts which are oriented normal to the tangent of the working perimeter. The teeth are preferrably monolithic and of a uniform size and shape, and are both angularly set and laterally displaced relative to the plane of the blade body.

This is a continuation of application Ser. No. 08/144,578 filed on Oct.28, 1993, now abandoned, which is a continuation of Ser. No. 07/657,565filed Feb. 19, 1991 now U.S. Pat. No. 5,283,935, which is a CIP of07/344,920 filed Apr. 28, 1989 now U.S. Pat. No. 5,054,177.

BACKGROUND OF THE INVENTION

The present invention relates to a new and uniquely constructed raspblade for use in tire buffing machines to properly precondition tires inpreparation for retreading. More particularly, the present inventionrelates to a tire rasp blade having a novel geometry and construction ofthe blade's working edge such that a greater number of teeth may beemployed in a particular blade while retaining adequate tooth size, thusachieving maximum cutting efficiency, a longer useful life and otherenhanced performance characteristics.

Tire rasp blades have been used for many years in the tire retreadingindustry. These blades are mounted to the rotating hub of the tirebuffing machine and, when engaged with the used tire carcass, they cutor shear segments of rubber from the tread surface area of the tire. Inthis way, the tire is "buffed" to remove the unwanted used tread and toachieve an evenly textured surface suitable for retreading.

There are several distinct performance characteristics that areimportant to the successful operation and use of such tire rasp blades.The speed or efficiency of rubber removal during the tire buffingprocess is very important; by removing the unwanted rubber tread fromthe tire more quickly, the labor cost associated with the retreadingprocess is reduced. It is also essential, however, that the tire raspblade exhibit good durability--that is, the teeth positioned on theblade should not bend, break, wear or otherwise fail prematurely. It isalso important that the blade not generate excessive heat during thebuffing operation, since the tire surface can be damaged or even burnedby increased temperatures with the result that an effective retread isnot possible. Other important performance characteristics include theefficient utilization of energy and the generation of relatively lownoise levels during operation. Finally, it is also very important thatthe tire rasp blade leave a certain well-defined texture on the surfaceof the tire carcass from which the unwanted rubber has been removed. Toorough a surface will result in a poor bond between the tire carcass andthe new tread, thereby causing premature failure of the retreaded tire.

A number of prior art tire rasp blades have been developed in an attemptto meet the performance characteristics noted above. Such rasp bladesare disclosed, for example, in U.S. Pat. Nos. 3,879,825; 4,021,899;4,091,516; and 4,283,819. Another tire rasp blade construction,representing an improvement over these prior art structures, isdisclosed in my U.S. patent application Ser. No. 07/166,176, filed Mar.10, 1988. There still exists a need, however, for an economicallyproduced tire rasp blade with excellent durability that removes rubberfrom the tire carcass at a faster rate, while providing an excellentsurface texture on the buffed tire, and while maintaining relativelylower buffing temperatures.

There is also a present need in the tire retreading trade for a moredurable, yet efficient tire rasp blade for use with both flat-faced andcurved-face buffing hubs. The durability of the tire rasp blade used incurved-face buffing hubs is particularly important because fewer numbersof blades contact the tire at any one time during the operation of thecurved-face hub, as compared to flat-faced hubs. Because a curved-facedbuffing hub offers certain advantages over flat-faced hubs, a moredurable, high performance blade for use in curved-faced hubs would makethese hubs more attractive as alternatives to flat-faced hub assemblies.

SUMMARY OF THE INVENTION

The present invention is directed to a tire rasp blade found to overcomethe problems associated with the prior art. The tire rasp bladeconstructed in accordance with the present invention is more efficientin removing rubber from the tread surface of the tire--it achievesrubber removal rates 50% to 100% greater than presently commercial tirerasp blades. It is also remarkably durable, with significantly lesstooth breakage and a substantially longer useful working life than knowncommercial tire rasp blades. These improved performance characteristicsare achieved, moreover, while still obtaining an excellent surfacetexture on the buffed tire and without generating excessive heat.

In accordance with the present invention, a tire rasp blade is providedfor use in a tire buffing machine, and particularly a circumferentialbuffing machine, to remove rubber from a tire carcass. The tire raspblade comprises an elongated body adapted for assembly in a rotating hubof the tire buffing machine and has a working portion including aplurality of uniformly and closely spaced teeth which together form anoutside arcuate working perimeter protruding from the hub. Each of theteeth has a base and a working edge and is separated from itsneighboring teeth by truncated generally elliptical primary cutoutsoriented generally normal to the tangent of the working perimeter. Eachof the teeth also has leading and trailing edges defined by theelliptical cutouts, with the leading edge and the working edge forming aleading angle having an apex that points in the direction of hubrotation, and the trailing edge and working edge forming a trailingangle having an apex that points away from the direction of rotation ofthe hub. Finally, the blade is symmetrical; that is, the tootharrangement is identical regardless of the direction of blade movementduring the buffing operation.

One of the important design principles of the present invention is theutilization of an increased number of teeth along the length of theblade achieved by novel tooth and blade geometry, while at the same timeretaining adequate tooth size and an optimum orientation of the teethrelative to both the blade body and each other so that each tooth maymost effectively address or attack the tire surface during the buffingoperation. Those of ordinary skill in the art will recognize that whilean increased number of teeth creates a greater potential for cuttingefficiency, this may requires the use of smaller teeth, more susceptibleto breakage. The present invention achieves the sought after balance ofa greater number of teeth, while retaining adequate tooth size.

In accordance with the present invention, each of these objectives isachieved by a tire rasp blade having all of its teeth arranged along theblade's working portion in uniformly and closely spaced relation--eachtooth being separated from its neighboring teeth by generally ellipticalshaped primary cutouts. These cutouts are oriented to be generallynormal to the tangent of the blade's working perimeter and are truncatedby the working perimeter so that the trailing and leading apexes ofneighboring teeth are closely spaced.

The teeth of the blade's working edge are also either laterallydisplaced or angularly set from the plane of the blade's body portion.Thus, the teeth are formed or bent at their base so that they arepositioned at an angle to the plane of the base. Moreover, the teeth maybe both laterally displaced and angularly set in such a manner thatapproximately one-half of the teeth is laterally displaced to one sideand the other half is laterally displaced to the opposite side, whilethe angularly set teeth are set in different complimentary angles to theplane of the blade's body. The lateral displacement and angular set ofthe teeth, together with the unique geometery of the blade's bodyportion, permit the use of the maximum number of teeth while stillachieving the balance of properties that are essential to satisfactoryblade performance.

In accordance with a preferred embodiment of the invention, the teethare laterally displaced and angularly set in groups or sets along theworking edge of the blade. Most preferably, the teeth are positioned ingroups of two, or pairs, with one tooth of a first pair being laterallydisplaced and the other tooth of that first pair being angularly set;then, in adjacent pairs, one tooth is laterally displaced in an oppositedirection from the tooth laterally displaced in the first pair, whilethe other tooth is angularly set in a complimentary position from theangularly set tooth in the first pair. In this fashion, the teeth willmost effectively address the rubber surface to be cut.

It has also been found in the practice of the present invention thatvarious elements of the blade's geometry play an important part inoptimization of blade performance. Moreover, the relationship of thesevarious elements is also significant to blade performance. Thus, thespacing between teeth (later defined as the "spacing angle") and thesize of the teeth (later defined as the "tooth size angle") and theirrelationship (later defined as the "tooth spacing to size ratio") allhave been found to effect blade performance.

Moreover, the relative size of the teeth and primary cutouts may also bedesigned to achieve both the necessary close spacing of the teeth andenhanced heat transfer properties. In accordance with this embodiment ofthe invention, the minimum width of the blade's teeth is between about80% and 110% of the maximum width of the primary elliptically shapedcutouts. This arrangement assures sufficient mass in the body of thetooth to achieve optimum strength and permit heat transfer ordissipation from the tooth's working edge through the base of the toothand into the blade's body portion and the metal rasp hub, which togetheract as a heat sink. As a result, the teeth remain cooler during thebuffing operation, giving the teeth greater durability and preventingheat build-up at the buffing interface between the blade and tire.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth in the appendedclaims. However, the invention's preferred embodiments, together withfurther objects and attendant advantages, will be best understood byreference to the following description taken in connection with theaccompanying drawings in which:

FIG. 1 is an end view of a conventional flat-faced circumferentialbuffing machine hub and blade assembly;

FIG. 2 is a side elevational view illustrating a tire rasp blade made inaccordance with one embodiment of the present invention;

FIG. 3 is an enlarged partial side elevational view of the working edgeof the rasp blade of FIG. 2, illustrating the blade P at an intermediatestage of manufacture in accordance with the present invention;

FIG. 4 is a partial plan view of the working edge of the rasp blade ofFIG. 3;

FIG. 5 is a plan view similar to that of FIG. 4, but showing the angularsetting of the teeth at a later intermediate stage of manufacture;

FIG. 6 is a plan view similar to FIGS. 4 and 5, but showing the angularsetting and lateral displacement of the teeth in the final constructionof the tire rasp blade according to one embodiment of the presentinvention;

FIG. 7 is a cross-sectional view taken along line 7--7 of FIG. 6 andshowing the angular set and lateral displacement of one tooth to oneside of the blade body;

FIG. 8 is a cross-sectional view similar to that of FIG. 7, but takenalong line 8--8 of FIG. 6, and showing the angular set and lateraldisplacement of another tooth to the opposite side of the blade body;

FIG. 9 is an end view showing the arrangement of the tire rasp blade ofthe present invention as mounted in a curve-faced tire buffing machinehub;

FIG. 10 is a side elevational view illustrating a tire rasp blade madein accordance with a particularly preferred embodiment of the presentinvention;

FIG. 11 is a partial enlarged side elevational view of FIG. 10 showingthe novel geometric configuration of the blade working portion;

FIG. 12 is a further enlarged side elevational view of FIG. 11illustrating the novel geometry of the blade teeth; and

FIG. 13 is a plan view of a particularly preferred embodiment of theworking perimeter of the rasp blade of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a buffing machine hub assembly, designatedgenerally as 20, is shown with a plurality of tire rasp blades 22 andspacers 24 mounted in a conventional operational arrangement. As can beseen, the blades 22 are mounted on the circumference of the hub atalternating angles to the direction of hub rotation. In this way, theblades create an oscillating, side-to-side action as the hub rotatesduring buffing. This is, of course, conventional and well known to thoseof ordinary skill in the art. As shown in FIG. 2, the tire rasp blade 22includes a body 32 and a working portion 34. It will be appreciated bythose skilled in the art that body 32 is generally planar and is adaptedfor assembly, by means of mounting holes 36 or 38, to the rotatable rasphub as illustrated in FIG. 1. When properly assembled to the hub of thebuffing machine the working portion has its outside arcuate workingperimeter 35 protruding from the hub. Of course, a set of blades 22 areused in the machine hub assembly and together they act to remove rubberfrom the used tire carcass and to condition the tire tread surface areain preparation for a subsequent retreading process.

The working portion 34 of blade 22 is the outer, arcuate part of theblade that contacts the tire and includes a unique arrangement of teeth40. The shape or geometric configuration of the teeth 40 may vary inaccordance with the teachings of the prior art, such as U.S. Pat. Nos.2,896,309; 3,082,506; 3,618,187; 3,879,825; 4,021,899; 4,059,875; and4,091,516, the disclosures of which are incorporated herein byreference. However, the close and uniform positioning of each toothrelative to its neighboring teeth, the uniform tooth configuration, thecombination of lateral displacement and angular set given to the teeth,and the use of generally elliptical and properly sized primary cutoutsare all novel and unique to the present invention.

The initial stage of manufacture for the tire rasp blade 22 of thepresent invention is clearly illustrated in FIGS. 3 and 4. At this stageof manufacture, the generally planar body 32 is provided with generallyelliptical primary cutouts 54 to form teeth 40. The teeth 40 aresubstantially the same size and configuration and each includes aworking edge 41 and a base 43 which joins the tooth to the body 32 ofthe blade. Each tooth also includes a leading edge 46 which togetherwith working edge 41 forms a leading angle "alpha". The leading angle"alpha" terminates in a leading apex 49 which points in the direction ofhub rotation. Each tooth also includes a trailing edge 48 which togetherwith working edge 41 forms a trailing angle "alpha". The trailing angle"alpha" terminates in a trailing apex 53 that points away from thedirection of hub rotation. These leading edges 46 and trailing edges 48are defined by the size and shape of the elliptical cutouts 54. Theterms "leading" and "trailing" find their significance in relation tothe movement of blade 22 as the rasp hub rotates. Blade movement, andhub rotation, are designated in the drawings by Arrow A. It is alsodesirable that each tooth include a centrally located semi-circular,v-shaped (or otherwise configured) cutout 50. This cutout 50 alsoprovides blunt edges 51 along the working perimeter at the circularcutouts. These blunt edges allow the tire surface to be "buffed" after aleading or trailing edge has cut it; they also do not allow portions ofthe steel blade to snag on the tire rubber surface to be cut. The use ofsuch a generally circular secondary cutout to form blunt edges 51 is,however, known to those of ordinary skill in the art.

Each of the primary cutouts 54 is generally elliptical in shape and isoriented such that its longitudinal axis is generally normal to thetangent of the working perimeter of the blade. The elliptical shape ofthe primary cutouts permits the use of teeth having sufficient size toachieve the desired strength while maintaining the desired closelyspaced relationship, the necessary heat transfer properties, and anincreased cutting efficiency. The elliptical cutouts 54 are truncated atthe perimeter of the blade; this truncation allows the creation of anoptimum angle "alpha", and still permits the closely spaced relation forleading and trailing apexes of neighboring teeth.

The use of novel, generally elliptical shaped primary cutouts allows theformation of various elements of the blade's working portion geometry,including the angles "alpha", "beta" and "omega" (see FIGS. 3, 11 and12). The novel elliptical shape, for example, permits the formation ofthe preferred ranges for the angle "alpha", which must be large enoughto avoid the "needling" effect which can occur with blade designs inwhich the leading and trailing apexes are so small as to be susceptibleto breakage. This generally elliptical shape also permits the formationof preferred ranges for the angle "beta", also called the teeth "spacingangle"--the angle defined by two radii having centerpoint "CP", one ofwhich, R1, intersects the apex of the trailing edge of one tooth, andthe other of which, R2, intersects the apex of the leading edge of thenext following tooth. The elliptical shape of the primary cutouts alsopermits the formation of preferred ranges for the angle "omega", alsocalled the "tooth size angle"--the angle defined by two radii havingcenterpoint "CP", one of which, R2, intersects the apex of the leadingedge of one tooth, and the other of which, R3, intersects the apex ofthe trailing edge of the same tooth.

Those of ordinary skill in the art will appreciate that the primarycutouts, while preferably elliptical, may also be merely generallyelliptical: thus, other closely related geometric configurations areacceptable, as long as they retain the curved, oval shape. This curvedoval shape is important, as it has been found that only this shapeallows the formation of "closely spaced" teeth as taught by the presentinvention, yet also preserves the adequate tooth size necessary toprevent breakage and impart significant heat transfer capabilities toindividual teeth.

One of the important design principles of the present invention is theuse of "closely spaced" teeth in conjunction with teeth of an adequatesize to reduce breakage while retaining cutting efficiency andsignificant heat transfer capabilities. Thus, the ratio of the spacingbetween adjacent teeth and the size of the tooth, also called the "toothspacing to size ratio" (which by reference to FIG. 11 can be termed theH/F ratio), is less than 20% and, in the particularly preferredembodiment, is less than 15%.

As previously stated, the teeth 40 are initially formed in accordancewith the present invention by first making the elliptical cutouts 54 inthe blade 22 so that the trailing apex of one tooth is immediatelyadjacent to or virtually contiguous with the leading apex of the nextfollowing tooth. In the preferred embodiment of the present invention,the span between the trailing and leading apexes of teeth 40, afterlateral displacement and angular setting, is less than about 0.025 inch.In the illustrated embodiment, the cutouts 54 are of substantially thesame size, shape and depth, thereby defining teeth of substantiallycommon size, configuration and height. Moreover, the spacing betweenneighboring teeth is kept to a minimum and is uniform from tooth totooth.

By constructing the working edge 14 of the blade with uniformly andclosely spaced teeth including the novel geometric configuration ofgenerally elliptical primary cutouts, a maximum number of teeth andleading edges can be employed per unit length of the blade, while stillpreserving adequate tooth size and strength, and promoting a moreaggressive action and faster rubber removal. And because more teeth aredoing the work of rubber removal, each tooth is subject to less stresswith the result that teeth of substantially the same configuration anddimension exhibit better wear, are more durable and less subject tobreakage as compared to prior art blades. Moreover, by constructing theteeth and elliptical cutouts so that the minimum width of the teeth isbetween 80% and 110% of the maximum width of the elliptical cutouts, asufficient amount of material is present in the "neck" of each tooth toefficiently transfer heat from the working edge 41 into the blade body32 and buffing machine hub, which together act as a substantial heatsink. Further, the tooth arrangement is symmetrical, i.e., the tootharrangement is identical regardless of the direction of blade movementduring the buffing operation. This symmetrical tooth arrangementprovides additional ease in operation, as the blades can thus be changedmore quickly.

Another facet of the present invention is that the teeth 40 have asubstantially monolithic construction; that is, the teeth have no holes,slits or other discontinuities between working edge 41 and base 43 toweaken the teeth or to inhibit heat transfer away from the workingperimeter of the blade. Thus, the rasp blade exhibits improveddurability and runs cooler even with a greater number of teeth per unitlength of the blade.

Still another facet of the tire rasp blade design of the presentinvention is the positioning and orientation of the teeth. It has beenfound in accordance with the present invention that that by laterallydisplacing some of the teeth from the plane of the blade body, andgiving other teeth an angular setting, a significant improvement inblade performance is achieved. As shown in FIGS. 6-8, the teeth may belaterally displaced to form an angle with the main plane P of blade body32. In addition, it has been found important to blade performance thatthe teeth be displaced and/or set to both sides of the blade body. Inthe preferred embodiment of the invention, the adjacent teeth aredisplaced in groups of two, or pairs.

In the context of the present invention the term "laterally displaced"is intended to refer to a tooth 40 which is bent or formed at its base43 so that the middlepoint of its free end 41 is offset relative to thecenterline of the blade body 32. In other words, and as shown in FIGS. 7and 8, the tooth 40 forms an angle D relative to the plane P of theblade body 32. In accordance with a particularly preferred embodiment ofthe present invention, the teeth 40 are laterally displaced from theirbase 41 at an angle of between 1° and 7° from the plane of the bladebody. It has been found that at angles larger than 7° the teeth are lessdurable, and, at angles smaller than 1° the blade is not as efficient inthe removal rate of rubber during the buffing operation.

In the context of the present invention the term "angularly set" isintended to refer to a tooth 40 that has been bent or formed at its base43 such that the leading edge 46 and trailing edge 48 of the same toothare on alternate sides of the centerline of the blade body 32, thoughthe middlepoint of the tooth's free end 41 remains on the centerline ofthe blade body 32. A tooth that has been angularly set may also belaterally displaced by bending or forming the angularly set tooth suchthat the middlepoint of its free end 41 is offset relative to thecenterline of the blade body 32. As shown in FIG. 5, this angularsetting is preferably made in a repeating series or cycle of four teeth.Thus, tooth 40A is angularly set across the plane of the blade and tooth40C is given an opposite angular setting. This cycle is repeatedbeginning with tooth 40E. Also, the teeth can be laterally displaced inpairs. Thus, as shown in FIG. 6, teeth 40A and 40B are displaced to oneside of the blade in the direction of arrow B, whereas teeth 40C and 40Dare displaced to the opposite side of the blade in the direction ofarrow C. Again, the cycle is repeated with the displacement of teeth 40Eand 40F in the direction of arrow B. This alternating lateraldisplacement is continued throughout the entire length of the blade 22.

When using closely spaced teeth, care must be taken to assure that'theirleading edges are positioned in relation to neighboring teeth toproperly address the tire surface for effective rubber removal. Thus,the trailing edge of one tooth must always be laterally displaced orangularly set on the opposite side to which the leading edge of the nextfollowing tooth is displaced or set. This tooth arrangement ensures thatthe leading and trailing apexes of each tooth, together with therespective trailing and leading edges, may be arranged to properlyaddress the tire for efficient rubber removal. Accordingly, in the nextphase of the manufacturing process, some of the teeth 40 are angularlyset relative to blade body 32 as illustrated in FIG. 5, while others arelaterally displaced across the plane of blade body 32.

All of these design parameters are employed in the tire rasp bladesillustrated in the drawings. The blade 22 shown in FIG. 2, for example,has a working perimeter 35 with a longitudinal (i.e. circumferential)dimension of approximately 7.0 inches. All of the teeth are closely anduniformly spaced along the length of the blade thereby permitting asmany as twenty-eight teeth in a single blade. There are also groups 56of two teeth displaced to one side along the blade's length, andalternating groups 58 of two teeth displaced to the opposite side. Eachof the teeth is bent from its respective base 43 at an angle ofapproximately between 1° and 7° from the plane of body 32.

Preferably, the elliptical cutout 54 has a longitudinal dimension Xwhich is about between 1.5 and 1.75 times its maximum width Y. Inaccordance with a particularly preferred embodiment of the invention,the longitudinal dimension of the cutout 54 is at least 0.200 inch whileits maximum width Y is about 0.120-0.130 inch and the minimum width Z oftooth 40 is about 0.110-0.120 inch. In this embodiment, the spacingbetween the leading and trailing apexes of neighboring teeth is aboutbetween 0.015-0.030 inch. In an exemplary embodiment, the spacingbetween the leading and trailing apexes of neighboring teeth is about0.020-0.030 inch. In this exemplary embodiment, the dimension of tooth40 along its working edge 41 from leading apex 49 to trailing apex 53 isabout 0.220-0.250 inch and cutout 50 has a diameter of about 0.090-0.120inch. Therefore, in this embodiment the spacing between leading andtrailing apexes of adjacent teeth is less than 20% of the tooth lengthalong its working edge 41.

FIGS. 10-13 illustrate a particularly preferred embodiment of thepresent invention. Thus, referring now to FIG. 10, a tire rasp blade 22has a working perimeter 34 with a longitudinal (i.e. circumferential)dimension of approximately 7.0 inches. This circumferential dimension isapproximately equal to the arc of a circle with a 9 inch diameter, withthe arc extending along one-fourth (90°) of the circle. Two otherpreferred embodiments (not disclosed in the drawings) include tire raspblades with a working perimeter whose circumferential dimensions areapproximately equal to the arc of a circle with an 11.5 inch diameter,with the arc extending along one-sixth (60°) and one-fifth (72°) of thecircle, respectively. Body 32 is again generally planar and is adaptedfor assembly, by means of mounting holes 86, to the rotatable rasp hubas illustrated in FIG. 1. All of the teeth are closely and uniformlyspaced along the length of the blade as described previously, therebypermitting twenty-eight teeth in the single blade. Referring now to FIG.13, there are also groups or pairs 76 of two teeth. These groups form arepeating pattern of four teeth with, for example, tooth 41M laterallydisplaced to one side along the blade's length, tooth 41N angularly setin one direction, and teeth 41O and 41P in an adjacent pair laterallydisplaced and angularly set in correspondingly opposite directions,respectively. Each of the laterally displaced teeth is bent from itsrespective base 43 at an angle of approximately between 1° and 7° fromthe plane of body 32. However, the middle group 77 of four teeth, of thetwenty-eight teeth show in FIG. 13, do not follow the above describedpattern. Instead, these teeth are alternately laterally displaced, withtooth 41Q laterally displaced "up", for example, and the next toothdisplaced "down". Additionally, the first tooth 41Q of the middle fourteeth is laterally displaced in the direction opposite to the lateraldisplacement of the second tooth 41R preceding it. This particularpattern of lateral displacement and angular setting has been found toprovide an extremely durable rasp blade which maximizes cuttingefficiency while employing a symmetrical tooth arrangement to achievethe necessary buffed tire surface.

Referring again to FIGS. 10-13, the particularly preferred embodimentwill now be more specifically and dimensionally described. Thus, R4, theradius measured from the center "CP" of the circle formed by extendingthe arcuate working edge is approximately 4.50 inch.

As explained above, the novel shape of the primary cutouts allows theselection of the preferred ranges for the angles "alpha", "beta" and"omega". Thus, "alpha" is about 35°, while its preferred working rangeis between 30° and 40°. It has been found that an "alpha" angle lessthan about 30° results in premature wear and tooth deformation whereasangles greater than about 40° reduce rubber removal efficiency andincrease operating temperatures. The spacing angle "beta" is about0.25°, while its preferred working range is less than 0.50°. It has beenfound that a "beta" angle above about 0.50° is too large and results intoo few teeth along the blade's working perimeter, thereby reducingrubber removal efficiency. Finally, the tooth size angle "omega"--isabout 3°, while its preferred working range is between about 2.75° and3.25°. When the "omega" angle is below about 2.75°, the teeth haveinsufficient strength and are subject to early failure, while anglesabove about 3.25° reduce the number of teeth per unit length of bladeand result in reduced rubber removal efficiency.

Still referring to FIGS. 10-13, tooth size is generally defined by thefollowing dimensions: 1) "F", the distance between leading and trailingapexes, is 0.230 inch; 2) "I", the distance along the working edge froma leading or trailing apex to the blunt edge 51 of a secondary circularcutout, is 0.070 inch; 2) Z1, the minimum width of a tooth, is 0.117inch; 3) X1, the longitudinal distance of the primary cutouts, is 0.209inch; and 4) Y1, the maximum width of the primary cutout, is 0.127 inch.These five parameters, "F", "I", "Zi", "Xi" and "Yi", together form ablade with sufficiently large teeth to resist wear and breakage andpromote heat transfer, yet provide closely spaced teeth to ensure amaximum number of teeth (the existence of which increases both cuttingefficiency and durability). In fact, the novel tooth configuration andblade geometry of the present invention allows truly "closely spaced"teeth: the distance "H" between the leading apex of one tooth and thetrailing apex of an adjacent tooth in the particularly preferredembodiment is about 0.023 inch. Thus, the H/F ratio for this embodimentis about 10%.

Referring still to FIGS. 10-13, the secondary cutouts are generallydefined by the following dimensions: 1) "J", the depth of the circularsecondary cutout, is 0.036 inch; 2) D2, the diameter of the circularsecondary cutout, is 0.094 inch; and 3) "G", the length of the circularcutout along the working perimeter, is 0.091 inch. These threeparameters, "J", "D2", and "G" together form a circular cutout withblunt edges for imparting a buffing action to the tire surface, yetstill allow the formation of a large, durable, tooth that cuts highlyefficiently and retains significant heat transfer capabilities.

This particularly preferred embodiment of the tire rasp blade of thepresent invention, described above, exhibits exceptional rubber removalrates when used in conventional buffing machines--as much as 50%-100%faster than the known higher performance prior art blades. As a result,significant labor savings can be achieved in the retreading process withvirtually no additional capital expense. Equally important, the bladeproduces a very high quality tread surface area texture withoutgenerating excessive heat. And all of this is achieved while retainingoutstanding durability--as much as 60%-100% longer useful life. Inshort, the tire rasp blade of the present invention significantlyoutperforms any other known prior art blade.

The tire rasp blade of the present invention finds particularlyadvantageous use in combination with circumferential buffing machinesand also curved face buffing machines. Moreover, it exhibits outstandingdurability and strength when used with well known problem tires, such ashigh mileage steel belted radial tires using high durometer rubbercompositions.

Of course, it should be understood that various changes andmodifications to the preferred embodiments described herein will beapparent to those skilled in the art. Such modifications and changes canbe made to the illustrated embodiments without departing from the spiritand scope of the present invention, and without diminishing theattendant advantages. It is, therefore, intended that such changes andmodifications be covered by the following claims.

I claim:
 1. A tire rasp blade for use in a tire buffing machine toremove rubber from a tire, said tire rasp blade comprising:an elongatedbody adapted for assembly in a rotating hub of the tire buffing machine;said body including a working portion comprising a plurality of closelyspaced teeth having substantially the same size and configuration andtogether forming an arcuate working perimeter protruding from the hub;each of said teeth having a base and a working edge and being separatedfrom neighboring teeth by truncated generally elliptical primarycutouts, the longitudinal axis of each of said cutouts being orientedgenerally normal to the tangent of said working perimeter, each of saidteeth also having leading and trailing edges defined by said cutouts,said leading edge and said working edge forming a leading angle having aleading apex that points in the direction of hub rotation, and saidtrailing edge and said working edge forming a trailing angle having atrailing apex that points away from the direction of hub rotation, saidleading and trailing angles being between about 30° and 40°; and saidteeth being uniformly and closely spaced so that the trailing apex ofeach tooth and the leading apex of the next following tooth form aspacing angle less than about 0.50°.
 2. The tire rasp blade of claim 1wherein said working portion includes at least 28 teeth.
 3. The tirerasp blade of claim 1 wherein said teeth are monolithic and the leadingand trailing apexes of each of said teeth are separated by generallycircular and truncated secondary cutouts.
 4. The tire rasp blade ofclaim 1 wherein said leading and trailing apexes of neighboring teethare within less than 0.030 inch.
 5. The tire rasp blade of claim 1wherein the length of each of said elliptical cutouts, measured along aline generally normal to the working perimeter, is greater than one andone half times the maximum width of each of said generally ellipticalprimary cutouts.
 6. The tire rasp blade of claim 1 wherein said leadingangle is approximately equal to said trailing angle.
 7. A tire raspblade for use in a tire buffing machine to remove rubber from a tire,said tire rasp blade comprising:an elongated body adapted for assemblyin a rotating hub of the tire buffing machine; said body having aworking portion comprising a plurality of uniformly and closely spacedteeth together forming an arcuate working perimeter protruding from thehub; each of said teeth having a base and a working edge and beingseparated from neighboring teeth by truncated generally ellipticalprimary cutouts, the longitudinal axis of each of said cutouts beingoriented generally normal to the tangent of said working perimeter, eachof said teeth also having leading and trailing edges defined by saidcutouts, said leading edge and said working edge forming a leading anglehaving a leading apex that points in the direction of hub rotation, andsaid trailing edge and said working edge forming a trailing angle havinga trailing apex that points away from the direction of hub rotation; anda first portion of said teeth being laterally displaced to one side ofsaid body and a second portion of said teeth being laterally displacedto the other side of said body, whereby said teeth form an angle to theplane of said body between about 1° and 7°.
 8. The tire rasp blade ofclaim 7 wherein said working portion includes at least 28 teeth.
 9. Thetire rasp blade of claim 7 wherein said teeth are monolithic and theleading and trailing apexes of each of said teeth are separated bygenerally circular and truncated secondary cutouts.
 10. The tire raspblade of claim 7 wherein said leading and trailing apexes of neighboringteeth are within less than 0.030 inch.
 11. The tire rasp blade of claim7 wherein the length of each of said elliptical cutouts, measured alonga line generally normal to the working perimeter, is greater than oneand one half times the maximum width of each of said generallyelliptical primary cutouts.
 12. The tire rasp blade of claim 7 whereinthe minimum width of each of said teeth is between 80% and 110% of themaximum width of each of said generally elliptical primary cutouts. 13.A tire rasp blade for use in a tire buffing machine to remove rubberfrom a tire, said tire rasp blade comprising:an elongated planar bodyadapted for assembly in a rotating hub of the tire buffing machine; saidbody having a working portion comprising a plurality of uniformly andclosely spaced teeth together forming an arcuate working perimeterprotruding from the hub; each of said teeth having a base and a workingedge and being separated from neighboring teeth by truncated generallyelliptical primary cutouts, the longitudinal axis of each of saidcutouts being oriented generally normal to the tangent of said workingperimeter, each of said teeth also having leading and trailing edgesdefined by said cutouts, said leading edge and said working edge forminga leading angle having a leading apex that points in the direction ofhub rotation, and said trailing edge and said working edge forming atrailing angle having a trailing apex that points away from thedirection of hub rotation; said teeth also being of substantially thesame size and configuration with a minimum width between about 80% and110% of the maximum width of each of said generally primary cutouts; andsaid teeth being arranged such that the trailing edge of each tooth ispositioned on the opposite side of the plane of said body to the leadingedge of the next following tooth.
 14. The tire rasp blade of claim 13wherein said working portion includes at least 28 teeth.
 15. The tirerasp blade of claim 13 wherein said teeth are monolithic and the leadingand trailing apexes of each of said teeth are separated by generallycircular and truncated secondary cutouts.
 16. The tire rasp blade ofclaim 13 wherein the length of each of said elliptical cutouts, measuredalong a line generally normal to the working perimeter, is greater thanone and one half times the maximum width of each of said generallyelliptical primary cutouts.
 17. A tire rasp blade for use in a tirebuffing machine to remove rubber from a tire, said tire rasp bladecomprising:an planar elongated body adapted for assembly in a rotatinghub of the tire buffing machine; said body having a working portioncomprising a plurality of uniformly and closely spaced teeth togetherforming an arcuate working perimeter protruding from the hub; each ofsaid teeth having a base and a working edge and being separated fromneighboring teeth by truncated generally elliptical primary cutouts, thelongitudinal axis of each of said cutouts being oriented generallynormal to the tangent of said working perimeter, each of said teeth alsohaving leading and trailing edges defined by said cutouts, said leadingedge and said working edge forming a leading angle having a leading apexthat points in the direction of hub rotation, and said trailing edge andsaid working edge forming a trailing angle having a trailing apex thatpoints away from the direction of hub rotation, said leading andtrailing angles being between about 30° and 40°; said teeth beinguniformly and closely spaced so that the trailing apex of each tooth andthe leading apex of the next following tooth form a spacing angle lessthan about 0.50°; said teeth also being of substantially the same sizeand configuration with a minimum width between about 80% and 110% of themaximum width of each of said generally primary cutouts; said teethbeing arranged such that the trailing edge of each tooth is positionedon the opposite side of the plane of said body to the leading edge ofthe next following tooth; and the tooth spacing to size ratio being lessthan about 20%.
 18. The tire rasp blade of claim 17 wherein said workingportion includes at least 28 teeth.
 19. The tire rasp blade of claim 17wherein said teeth are monolithic and the leading and trailing apexes ofeach of said teeth are separated by generally circular and truncatedsecondary cutouts.
 20. The tire rasp blade of claim 17 wherein saidleading and trailing apexes of neighboring teeth are within less than0.030 inch.
 21. The tire rasp blade of claim 17 wherein the minimumwidth of each of said teeth is between 80% and 110% of the maximum widthof each of said generally elliptical primary cutouts.
 22. The tire raspblade of claim 17 wherein said leading angle is approximately equal tosaid trailing angle.
 23. A tire rasp blade for use in a tire buffingmachine to remove rubber from a tire, said tire rasp blade comprising:anelongated body adapted for assembly in a rotating hub of the tirebuffing machine; said body having a working portion comprising aplurality of uniformly and closely spaced teeth together forming anarcuate working perimeter protruding from the hub; each of said teethhaving a base and a working edge and being separated from neighboringteeth by truncated generally elliptical primary cutouts, thelongitudinal axis of each of said cutouts being oriented generallynormal to the tangent of said working perimeter, each of said teeth alsohaving leading and trailing edges defined by said cutouts, said leadingedge and said working edge forming a leading angle having a leading apexthat points in the direction of hub rotation, and said trailing edge andsaid working edge forming a trailing angle having a trailing apex thatpoints away from the direction of hub rotation; said teeth also being:substantially the same size and configuration so that the leading apexand trailing apex of each tooth form a tooth size angle between about2.75 degrees and 3.25 degrees; and the tooth spacing to size ratio beingless than about 20% wherein the minimum width of each of said teeth isbetween 80% and 110% of the maximum width of each of said generallyelliptical primary cutouts.